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I observed this while on a flight that took of shortly after it had rained, but could not understand why it happened.

The windows of the aircraft had drops of water on the outside. As the flight moved on the runway and took off, I saw that water from the front side of the window (orientation with respect to the aircraft) was flowing towards the rear of the window, which was not surprising. However, I also noticed that it moved at an angle - the water from the lower end of the window was flowing towards the upper end. In other words, water was flowing diagonally across the window in the direction pertaining to flowing from the front bottom to the top rear.

As the plane was taking off, shouldn't its acceleration have been in a direction forward and upward? Then, shouldn't the drops have moved from the front top end to the bottom rear end? How can this be explained?

Thank you.

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  • $\begingroup$ The flow of air along the fuselage may have been affected by the position of the wing, amongst other things. Were you sitting behind the wing, assuming it was a standard wing layout, such as a Boeing 737? $\endgroup$
    – user108787
    Commented Jul 23, 2016 at 11:02
  • $\begingroup$ @count_to_10 No, it was before the wing. $\endgroup$
    – GoodDeeds
    Commented Jul 23, 2016 at 11:12
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    $\begingroup$ Aircraft do not fly in a level attitude. Especially when they are flying at slow speed, such as during takeoff and landing, they are in a nose-up attitude. I think that accounts for the wind direction you see. $\endgroup$
    – Mike Dunlavey
    Commented Jul 25, 2016 at 11:56

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My apologies for a short answer, but it really depends on many factors I don't know about, such as virtually anything that may have disturbed the airflow along the fuselage.

enter image description here

enter image description here

These extracts are based a pdf file from the University of Leipzig but unfortunately I can't get my tablet to copy the url.

My basic point is that, despite the direction of the acceleration of the aircraft, the airflow along the fuselage need not be parallel to the midline of the fuselage, and that this "opposite" flow may have easily overcome other forces, especially at the high take off speeds of modern jets.

What would useful to know if it was just your window, indicating a local airflow disturbance, or all along the aircraft.

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  • $\begingroup$ Thank you for your answer. I don't know if it was all along the aircraft, as I couldn't see the other windows along the aircraft from my seat (obviously). $\endgroup$
    – GoodDeeds
    Commented Jul 23, 2016 at 12:16
  • $\begingroup$ I would imagine it was all along the aircraft, but I will check myself on my next flight. As a kid, I got to visit the cockpit regularly and I once saw St Elmo's fire on the front windshield, it's quite impressive. $\endgroup$
    – user108787
    Commented Jul 23, 2016 at 12:22

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